<html>
<head>

<script language="Javascript">

function checkUserName (ssn) (

if (ssn.length <3 | | ssn.length> 18) (
/ / alert ( "\ Please enter the correct user name, user name, a length of 3-18 bit!")
document.getElementById ( "usernameErr"). innerHTML = "<font color='red'> Please enter the correct user name, user name, a length of 3-18 bit! </ font>";
document.getElementById ( "usernameErr"). focus ()
return false;
)

document.getElementById ( "usernameErr"). innerHTML = "";

return true;
)
</ script>
</ head>
<body>
<form method="post">
<input type="text" name="username"> <span> </ span>
<input type="submit">

</ form>
</ body>
</ html>

================================================== =================

To do their own thing, that is, a simple effect, have done before, then forget that they are also a few days, the help of classmates at the finish